This invention relates to an improved article for preparing critical surfaces. More particularly, the invention relates to an improved article for polishing, especially for polishing lenses.
Passive tool surfacings, such as wool, felt, silk, velveteen, leather, velour, cloth, pitch, pyroxylin coated fabrics, solvent leached urethane coated fabrics (poromeric suede) and flocked fabrics have been used in combination with polishing slurries to facilitate critical surface preparation or, more specifically, to produce a polished surface on glass, plastic, metal, ceramic and semiconductor materials, metallurgical and geological specimens, quartz, semi-precious stones, piezoelectric crystals and so forth. While efforts have been made for well over twenty years to incorporate polishing abrasives into a matrix to create an active "fixed abrasive" polishing tool, pad or surface, all past efforts have resulted in essentially complete encapsulation of the polishing abrasive whereby the identity and activity of the polishing abrasive have been lost, the polishing abrasive becoming, in effect, a passive filler.
In U.S. Pat. No. 2,865,725 there is disclosed a lens polishing article comprising a cotton fabric coated on at least one side with an abrasive substance comprising cellulose nitrate, a solvent and cerium oxide. Unfortunately, in actual practice the cerium oxide becomes encapsulated in the cellulose nitrate rendering the cerium oxide essentially useless as an abrasive.
U.S. Pat. No. 3,959,935 discloses a pad for grinding lens blanks in which the grinding abrasive is fixed to a surface of the pad. In grinding, however, the particles of abrasive used are substantially coarser than the particle size of abrasive used for polishing. Of course, encapsulation of larger particles is much easier to avoid than encapsulation of smaller particles. Also, grinding is based on mechanical stock removal only, permitting the use of firmly bonded abrasive grains or particles.
U.S. Pat. No. 3,230,672 discloses a "fining," i.e., fine grinding sheet comprising a mesh fabric having interstices, a layer of stabilized latex bonding material on one side of the fabric and partly in the interstices of the fabric and grit particles embedded in the bonding material and yieldingly supported thereby, the particles being preponderantly characterized by having flat plan facets thereon and by being oriented to present the flat plane facets substantially in a common plane parallel to the fabric, corners and edges of the particles being disposed laterally of the fabric and downward toward and into the interstices. The latex is not hydrophilic, and it is required that the grit particles be of a certain configuration and a certain orientation relative to the fabric.
U.S. Pat. No. 3,491,495 discloses a cleaning towel comprising a highly absorbent web coated with a dry cleaning composition including a binder, a relatively porous and absorbent low bulk density cleaning powder and a relatively non-porous and non-absorbent high bulk density carrier powder. The carrier powder is present in an amount sufficient to inhibit the tendency of the cleaning powder to dry out a coating slurry of the cleaning powder and carrier powder in a liquid vehicle. At least 40% by weight of the particles are in the 10 to 40 micron size range. Such a product is unsuitable for preparing, i.e., polishing, critical surfaces.
It is an object of the invention to provide an improved abrasive article for preparing critical surfaces on the surface of which article is carried a polishing abrasive. The polishing abrasive adheres to or is partially embedded in but free rolling on the surface of the article and thereby is effective for polishing. It is a more particular object of the invention to provide such an improved article for polishing critical surfaces, especially for polishing lenses. It is a further object of the invention to provide an improved abrasive article for producing a polished surface on glass, plastic, metal, ceramic and semi-conductor materials, metallurgical and geological specimens, quartz, semi-precious stones, piezoelectric crystals and so forth.
Other objects and advantages of the invention will be apparent from the following description.